Sepsis is a guaranteed USMLE topic because it tests recognition, a time-critical resuscitation bundle, and the hemodynamics of shock. This review covers sepsis and septic shock the way the boards test it, reflecting the Surviving Sepsis Campaign and current US practice. Follow current guidelines and institutional protocols clinically; this reflects guidance as of mid-2026.
Definitions
Under the Sepsis-3 framework, sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection, operationalized as an increase in the SOFA score of 2 or more points. Septic shock is the subset with circulatory and metabolic derangement severe enough to substantially increase mortality, defined clinically as a need for vasopressors to maintain a mean arterial pressure (MAP) of 65 mmHg or higher together with a lactate above 2 mmol/L despite adequate fluid resuscitation. The older SIRS criteria — temperature, heart rate, respiratory rate and white-cell count — are sensitive but nonspecific, and have been de-emphasized in favor of organ-dysfunction-based definitions, though they remain useful for screening.
Recognition
Suspect sepsis in any patient with a known or likely infection plus signs of organ dysfunction — altered mental status, tachypnea, hypotension, oliguria, or mottled skin. The qSOFA score (altered mentation, a respiratory rate of 22 or more, a systolic BP of 100 or below) flags higher risk, but current guidance recommends against using qSOFA alone as a screening tool; it is best used alongside broader screening. Lactate serves as both a severity marker and a resuscitation target. Common sources include the lungs (pneumonia), urinary tract, abdomen, skin and soft tissue, and indwelling catheters or lines, and identifying the source guides both antibiotics and the need for source control. Certain patients are especially vulnerable — older adults, the immunocompromised, those on chemotherapy or steroids, and people with indwelling devices — and warrant a lower threshold for suspicion.
Workup
Alongside cultures and lactate, the workup includes a complete blood count, a comprehensive metabolic panel, coagulation studies, and imaging directed at the suspected source, such as a chest radiograph or CT. The SOFA score aggregates dysfunction across respiratory, coagulation, hepatic, cardiovascular, neurologic and renal systems to quantify severity.
Management: the Hour-1 bundle
The single most testable element is the Surviving Sepsis Campaign Hour-1 bundle, initiated as soon as sepsis or septic shock is recognized:
- Measure lactate, and remeasure it if the initial level is above 2 mmol/L.
- Obtain blood cultures before giving antibiotics.
- Administer broad-spectrum antibiotics.
- Begin rapid crystalloid — at least 30 mL/kg — for hypotension or a lactate of 4 mmol/L or higher, within the initial 3 hours.
- Apply vasopressors if the patient remains hypotensive during or after fluids, to maintain a MAP of 65 mmHg or higher.
Beyond the bundle, the boards test the vasopressor of choice: norepinephrine is first-line in septic shock. Vasopressin is added next, and epinephrine after that; dopamine is reserved as an alternative and carries a higher arrhythmia risk. Source control — draining an abscess, removing an infected line, relieving an obstruction — is essential alongside antibiotics. Cultures should never delay antibiotics when the patient is unstable. Empiric antibiotic choice is broad initially and tailored to the likely source and local resistance patterns, then de-escalated once cultures return. Corticosteroids (IV hydrocortisone) are added in septic shock that remains vasopressor-dependent despite adequate fluids and pressors. Reassess frequently — perfusion, lactate clearance, urine output and mental status — and escalate to the ICU early.
Pathophysiology and complications
Sepsis reflects a dysregulated immune response to infection, with widespread cytokine release, endothelial injury, vasodilation and capillary leak producing distributive shock — warm shock with low systemic vascular resistance and a high cardiac output early on. Microvascular thrombosis and hypoperfusion then drive multi-organ dysfunction: acute kidney injury, acute respiratory distress syndrome, disseminated intravascular coagulation, hepatic dysfunction and altered mentation. Recognizing the warm, vasodilated picture distinguishes septic (distributive) shock from cardiogenic and hypovolemic shock, which are cold and vasoconstricted.
High-yield exam points and traps
- The Hour-1 bundle is the core answer: lactate, cultures before antibiotics, broad-spectrum antibiotics, 30 mL/kg crystalloid for hypotension or a lactate of 4 or more, and vasopressors to a MAP of 65.
- Norepinephrine is the vasopressor of choice in septic shock — a classic single-best-answer.
- Obtain cultures before antibiotics, but never delay antibiotics in an unstable patient to do so.
- Septic shock requires both vasopressors for a MAP of 65 and a lactate above 2 despite fluids — distinguishing it from sepsis without shock.
- qSOFA is no longer recommended as a standalone screen.
- A normal blood pressure does not exclude sepsis; young patients compensate until late.
- Distinguish distributive (septic) shock — warm, with low systemic vascular resistance — from cold cardiogenic and hypovolemic shock.
- Add hydrocortisone for septic shock that stays vasopressor-dependent despite fluids and pressors.
- Source control — draining or removing the focus — is as important as antibiotics.
Common questions
What is the Hour-1 bundle? Measure lactate, obtain blood cultures before antibiotics, give broad-spectrum antibiotics, start at least 30 mL/kg crystalloid for hypotension or a lactate of 4 mmol/L or higher, and apply vasopressors to maintain a MAP of 65 mmHg or higher.
Which vasopressor is first-line in septic shock? Norepinephrine; vasopressin and then epinephrine are added if needed, and dopamine is reserved as an alternative because of arrhythmia risk.
How is septic shock defined? A need for vasopressors to maintain a MAP of 65 mmHg or higher plus a lactate above 2 mmol/L despite adequate fluid resuscitation, under Sepsis-3; it carries substantially higher mortality than sepsis without shock.
Should cultures delay antibiotics? No — obtain cultures before antibiotics when feasible, but in an unstable patient antibiotics must not be delayed.
What lactate level matters? A lactate above 2 mmol/L is significant and is remeasured; a lactate of 4 mmol/L or higher triggers aggressive fluid resuscitation and marks higher mortality.
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